Field of the Invention
The present invention relates to a heating member for heating a workpiece such as a semiconductor wafer and to an electrostatic chuck and a ceramic heater which include the heating member.
Description of Related Art
Conventionally, a semiconductor fabrication apparatus has performed, for example, dry etching (e.g., plasma etching) on a semiconductor wafer (e.g., a silicon wafer). Since, in order to enhance accuracy of dry etching, the semiconductor wafer must be securely fixed, an electrostatic chuck has been proposed as means for fixing the semiconductor wafer. The electrostatic chuck fixes the semiconductor wafer by electrostatic attraction.
Specifically, the electrostatic chuck, for example, has an internal chucking electrode in a ceramic substrate formed of laminated ceramic layers. By use of electrostatic attraction generated through application of voltage to the chucking electrodes, the electrostatic chuck chucks the semiconductor wafer on one surface (a chucking surface) of the ceramic substrate. Usually, a metal base is bonded to the other surface (bonding surface) of the ceramic substrate.
Also, a certain known electrostatic chuck has a function of adjusting the temperature of (heating or cooling) a semiconductor wafer chucked on the chucking surface. For example, according to a known technique, a heat-generating element (e.g., a linear heat-generating pattern) is disposed in the ceramic substrate, and the heat-generating element heats the ceramic substrate to thereby heat the semiconductor wafer on the chucking surface. Also, according to another known technique, a cooling path is provided in the metal base for flowing cooling fluid therethrough to thereby cool the ceramic substrate.
Further, according to a technique disclosed in recent years for making the temperature of the chucking surface (i.e., in-plane temperature) two-dimensionally uniform, a conductive layer in the form of a land pattern and which partially constitutes an electricity supply path for supplying electric power to the heat-generating element is disposed in layers (e.g., two layers) in the ceramic substrate (see Patent Document 1).
According to this technique, for example, two conductive layers are disposed at different positions in the thickness direction and have the same planar shape (i.e., the shape projected in the thickness direction) along the ceramic layers and the same external dimension. Also, vias are formed along the thickness direction for electrically connecting the two conductive layers.
In the case where two conductive layers are provided in the ceramic substrate as mentioned above, the ceramic substrate is manufactured, for example, as follows: ceramic green sheets on which patterns that are to become conductive layers are formed respectively are laminated together, followed by firing.